Research is proposed in four specific enzyme mechanism problems where the enzymes catalyze metabolically important but chemically unobvious transformations. In each case design and testing of suicide substrates as mechanistic probes and potentially useful selective inhibitors are featured as part of the investigations. 1) Enzymic cleavage of 1-amino-1-carbosy-cyclopropane, a precursor of the fruit-ripening hormone ethylene, will be studied to analyze how the cyclopropane is activated for fragmentation in bacterial and plant metabolism. 2) The glutamine-dependent aromatizing aminations catalyzed by anthranilate synthetase and PABA-synthetase will be probed with pure enzymes and substrate analogs and reaction intermediates. 3) We will analyze pure hepatic cytochrome P450 isozymes for selectivity in processing and routes of suicidal autoinactivation with a) olefinic and acetylenic barbiturates, b) 17-d-ethynyl steroids c) the 7-thioacetyl steroid diuretic spironolactone. 4) The molecular mechanism of bacterial resistance to organomercurials involves the novel enzyme activity organomercury lyase. We plan to purify the enzyme and analyze the mechanism of cleavage of the cargon-mercury bond.